
here it is the bug reported by someone and now I added to it:
https://bugzilla.kernel.org/show_bug.cgi?id=72701#c15

====so that's not the commit:
NOPE:apparently this commit, added the patch which makes my system hang:
https://github.com/torvalds/linux/commit/f2bc561610962693be61425cf913778586d8f9c1
also bug is here:
https://bugs.freedesktop.org/show_bug.cgi?id=75917

trying to see if commenting those 2 lines of the patch will fix it: -> nope, it didn't fix it! must not be this! looks like this was added after 3.15.4 so... crap
then trying without commenting(edit:actually with them commented) those 2 lines(so leaving the patch in) but with radeon.runpm=0
kernel command line: -> yes it does work with this kernel command line!



====
ok found it, it's because of vgaswitcheroo ! if this setting is enabled in 3.15.4 it will lockup
but if it's enabled in 3.12.23 it won't!
so something must've changed in this switcheroo code between 3.12 and 3.15 also 3.16-rc4 has it!

===========
with the .config#22*
included in current folder, and when both graphics cards are enabled in bios
it will lock up after a certain time when booting up

even tho i disabled tlp (powersaving features)

and even when radeon is built into kernel, then only when I add the firmware:
radeon/BTC_rlc.bin
only then it locks up! without it, it works, but ofc, the card is not seen
but in kernel 3.12 stock manjaro 3.12.24-1-MANJARO 
with this one works, and i can even see the temperature with sensors of the discrete card

the internal(APU) gfx card works by itself, alone.

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i don't get it :) why would it just work with 3.12 but not 3.15.4
